As device dimensions shrink, high dielectric constant (high-k or hi-k) materials are being used as the gate dielectric for devices operating at the lowest voltages in the circuit, henceforth referred to as core devices. But at least three problems exist if a high-k material, such as HfO2 (hafnium oxide), is used for high voltage devices, such as an intermediate thickness gate oxide devices (henceforth known as TGO devices), a thicker gate oxide devices (henceforth known as DGO devices), or capacitors. First, if HfO2 is formed over SiO2 (silicon dioxide), the Hf (hafnium) and Hf-induced defects may diffuse into the SiO2 during manufacturing. The diffusion will cause poor reliability, especially in high voltage applications. Second, using a high-k material changes the work function of the device. When the work function changes, the technology associated with the device must be altered. Instead, by not changing to a high-k material, the earlier technology can continue to be used and time is saved having to develop any new technology. Third, it is unknown if any effects due to interaction between the high-k material and the other materials at the edge of the patterned gate are created when using HfO2 in a high voltage device. Thus, it is desirable to not use high-k materials for some semiconductor devices, such as high voltage devices.
It is often desirable that both core devices and high voltage devices are formed on the same semiconductor substrate. When forming the high-k material for the core devices, it is desirable to prevent the high-k material from being formed as part of a gate stack for the high voltage devices. Thus, there is a need for an integration process that enables the different dielectrics to be formed in different areas of the substrate.
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